LIght Dimmer Circuit Using DIAC And TRIAC

It Includea the details and Circuit explanation of how a LIGHT DIMMER Circuit works.

- Er. Parth Patel

1. Light Dimmer Circuit Prepared by :- Parth D. Patel (1401101090 39) Jay j. Patel (1401101090 34) Batch : C109 Basic Electronics OEP

2. The Circuit Diagram

3. The Components Used : Resistors : - 100 Ω - 2Watt - 4.7 kΩ - 0.5 Watt - 1 MΩ - 0.5Wat   Capacitors : - 0.1 μF – 400 V - 0.1 μF – 400 V - 0.1 μF – 400 V    TRIAC : TLC 22238 DIAC : DB3 Variable Resistance : 500 kΩ

4. The Working Of Circuit A light dimmer works by essentially chopping parts out of the AC voltage. This allows only parts of the waveform to pass to the lamp. The brightness of the lamp is determined by the power transferred to it, so the more the waveform is chopped, the more it dims . Mains power is comprised of an alternating current that flows in one direction and then in the other, along the cable, at the rate of 50 or 60 cycles per second (known as Hertz ). By chopping the waveform at the zero-crossing point, smooth dimming can be achieved without the lamp flickering .

5.   The mains sine wave, and a phase-controlled waveform. The Alternating Current Wave form The choped waveform at zero point where smooth dimming is achived

6. The Imperative Components DIAC (DB3) TRIAC ( TLC 22238 )

7. The DIAC The DIAC is a full-wave or bi-directional semiconductor switch that can be turned on in both forward and reverse polarities. The DIAC gains its name from the contraction of the words  DIode  Alternating Current . The DIAC is widely used to assist even triggering of a TRIAC when used in AC switches . DIACs are mainly used in dimmer applications and also in starter circuits for florescent lamps .

8. Operation : The DIAC conducts a break-over voltage. When the device excceds thr break over voltage , it enters the region of negative dynamic resistance. The diode remains in its conduction state untill the current through it drops below what is termed the holding current. Below the holding current , the DIAC reverts to its hhigh resistance. Its behaviousr is bi-directional and therefore its operation occurs on both halves on AC Cycle.

9. The TRIAC The TRIAC is a three terminal semiconductor device for controlling current. It gains its name from the term   TRIode for Alternating Current. It is effectively a development of the SCR or thyristor , but unlike the thyristor which is only able to conduct in one direction, the TRIAC is a bidirectional device. The TRIAC is an ideal device to use for AC switching applications because it can control the current flow over both halves of an alternating cycle.

10. Opreation : It can be imagined from the circuit symbol that the TRIAC consists of two thyristors back to back but with a common gate terminal, and the cathode of one thyristor connected to the anode of the other, and vice versa . When the voltage on the MT1 is positive with regard to MT2 and a positive gate voltage is applied, one of the SCRs conducts. When the voltage is reversed and a negative voltage is applied to the gate, the other SCR conducts. This is provided that there is sufficient voltage across the device to enable a minimum holding current to flow .

11. Thank You